Mostly tradition. Asteroids have had their volatiles baked off their surface, or never had them due to forming inside the frost line. But it’s not a very intrin

Mostly tradition. Asteroids have had their volatiles baked off their surface, or never had them due to forming inside the frost line. But it’s not a very intrinsically meaningful distinction—it’s more about what they look like from the vantage point of Earth as they come by on close approach.